The present invention relates generally to the production of foundry molds by utilization of molding machines which include a pattern device, a molding box arranged thereon and a frame attached on the molding box. More specifically, the invention relates to devices wherein an excess of molding sand above that required for the production of a mold is initially introduced above the pattern device, and only a single compression is effected.
A method for filling granular materials into molding boxes is known from Swiss Pat. No. 301,031, wherein after filling the filled-in material is precompressed by inertia forces acting perpendicular to the pattern plane. Subsequently, the material is compressed again using a hopper containing a granular material and provided with a bottom closure whose outflow cross section corresponds substantially to the inside cross section of the molding box. This hopper is attached on the molding box during the filling of the latter, and the precompression is effected with the hopper attached. In this method, more granular material is fed to the hopper than is required for the production of the mold, and the excess sand is separated between the precompression and the secondary compression by slicing plates forming the closure of the hopper.
The attachable hopper has on its underside a reinforced edge so that a sand bed surmounting the box edge is formed before the secondary compression (see "Giesseri", 1957, p. 564,578, FIG. 7e, paper by Obering, Walter Goetz).
Furthermore a method for the mechanical production of molds from granular material is known from Swiss Pat. No. 308,043 where the granular material is precompressed by jarring with the frame attached, and after the precompression the excess sand is separated and the frame lifted, after which the mold is subjected to secondary compression with the frame lifted.
A molding machine with a sand stripper is also known from Swiss Pat. No. 537,222 wherein the excess sand level is stripped off between the precompression and the secondary compression above a certain amount parallel to the upper edge of the molding box.
As has been shown in the paper by Goetz referred to above, particularly FIG. 8 thereof, which also applies to the embodiments according to Swiss Pat. Nos. 308,043 and 537,222, a decisive improvement of the compression can be achieved under these conditions for the pattern device represented in FIG. 5. In order to achieve this uniformity of compression, an effective or intensive precompression of the filled granular material with the attached hopper is necessary before the excess molding sand is removed, and subsequently the secondary compression must be effected with the hopper lifted.
The present invention is aimed toward enabling production of molds of more uniform compression than is presently possible from clay-bonded granular material, if pattern devices having high patterns or considerable depressions must be utilized.
Another object is to considerably increase the number of molds that can be produced hourly for each pattern device without reducing their quality regarding uniform compression.
A further object is to omit the precompression of the molds by jarring with a sand bucket or sand frame attached, in order to avoid the secondary movements of the molding box and of other parts resting on the latter relative to the pattern device, which are caused by elastic deformation. These secondary movements can cause cracking of mold edges during the precompression by jarring, and they are also the cause of the annoying noise as well as of the excess wear on pattern devices, molding boxes, etc.
Another object is to substantially simplify existing methods in order to considerably reduce the investment costs for such plants and to reduce the maintenance costs in operation.